1. Field of the Invention
The present invention relates to a liquid application apparatus and a printing apparatus, and more particularly, to a liquid application apparatus and a printing apparatus for applying a liquid to a printing medium for a predetermined purpose of accelerating coagulation of ink and the like.
2. Description of the Related Art
At present, spin coater, roll coater, bar coater, and die coater systems have been known as systems for applying a liquid or material in a liquid state to printing media to be printed by printing apparatuses. These systems assume continuously performing application to a relatively long applied medium. Therefore, when, for example, relatively small sized applying media are intermittently transferred and application is performed for these printing media, a uniform coating film may not be obtained for each applied medium due to disturbance in a coating bead at positions to start and end application thereof or the like.
As a method for solving such a problem, for example, Japanese Patent Laid-Open No. 2001-70858 discloses a method that uses a rotating rod bar in a die coater system. In the method using a rod bar, an application liquid is discharged from a discharging slit onto the rod bar to form a coating film on the rodbar. Then, the formed coating film contacts an applied medium to be transferred as a result of a rotation of the rod bar. In such a method, when the coating film formed on the rod bar is not transferred or applied to an applied medium, the application liquid returns into a head due to a rotation of the rod bar and is recovered via a recovering slit. More specifically, the rod bar continues to rotate even at the non-application time, and the application liquid has formed a coating film on the rod bar. This makes it possible, even when applying media are intermittently supplied and application is intermittently performed for those, to obtain a uniform coating film.
In addition, for example, Japanese Patent Laid-Open No. 2002-517341 discloses a technique which uses a doctor blade being in contact with a roller for accumulating an application liquid between the blade and roller, and imparts the application liquid to the roller as a result of a rotation of the roller. In the present technique, as a result of a rotation of the roller, the application liquid that has been imparted is transferred and applied to a support to be conveyed between the roller and another roller. Further, Japanese Patent Laid-Open No. H08-72227 (1996) discloses a mechanism that applies in advance a processing liquid (application liquid) to insolubilize a dye prior to printing. In the technique, the application liquid in a replenishment tank is drawn out by being adhered to a rotating roller, and the drawn-out application liquid is simultaneously applied to a printing medium.
According to each of the techniques disclosed in the above patent documents, while a rod bar or a roller rotates, an application liquid is imparted and supplied to the surface of the bar or roller. A part opened to the atmospheric air or communicated therewith performs the imparting and supplying. Therefore, the application liquid possibly evaporates. Moreover, when the apparatus is changed in posture, the application liquid may leak accordingly.
To cope therewith, it has been known to seal a part to impart and supply a liquid such as ink to a roller. In, for example, an apparatus disclosed in Japanese Patent Laid-Open No. H08-58069 (1996), an ink chamber having doctor blades is abutted against the peripheral surface of a roller to thereby form a liquid chamber (ink reservoir) with respect to the roller. This allows suppressing evaporation and leakage of the liquid.
Further, an apparatus disclosed in Japanese Patent Laid-Open No. 2005-254229 can, by abutting an annular-shaped member against a roller to form a hermetically-sealed region to hold an application liquid, prevent the liquid from evaporating.
However, in the application mechanisms disclosed in Japanese Patent Laid-Open No. H08-58069 (1996) and Japanese Patent Laid-Open No. 2005-254229, the application liquid is to remain on the doctor blade that scrapes away the application liquid or the seal plate. Although it is possible to reduce the same by utilizing an interval regulating plate or by using a water-repellent material, the application liquid remains in a nip portion between the application member and liquid chamber and the vicinity thereof. When the apparatus is kept stopped in this state for an extended period of time, the application liquid interposed between the application member and liquid chamber and in the vicinity thereof may be increased in viscosity so that the application liquid is fixedly adhered. In the case of an increase in viscosity and fixed adhesion of the application liquid in the nip portion between the application member and liquid chamber, a large amount of application liquid adheres to only a part, on the application member, corresponding to the nip portion with the liquid chamber, and it becomes difficult to form a uniform layer on the surface of the application member. Therefore, the application liquid may partially become nonuniform.
To cope therewith, a technique disclosed in Japanese Patent Laid-Open No. 2002-96452 discloses a unit for performing a roller rotating operation at regular time intervals in a standby state for a printing operation so as to prevent fixed adhesion. In a printing apparatus disclosed in Japanese Patent Laid-Open No. 2002-96452, by performing an idle rotation of a roller at regular time intervals during standby for a printing operation, an application liquid increased in viscosity that has been adhered on to the roller is returned to a normal viscosity. Then, by separating the opposed roller at the elapse of every regular time interval, the application liquid is suppressed from fixedly adhering to the nip portion.
However, according to the technique disclosed in Japanese Patent Laid-Open No. 2002-96452, since the operation is performed at the elapse of every regular time interval during standby, the longer the standby time, the more power consumption increases. Moreover, when the apparatus is left in a power off state, a mechanism such as a built-in power becomes necessary. Further, since the opposed roller is separated at the elapse of every regular time interval, a mechanism to separate the roller becomes necessary besides an ordinary application mechanism, so that the mechanism of an application apparatus is complicated, and it may be inevitable to increase the size of the apparatus.